Many devices that employ magnetic fields have heretofore been encumbered by massive solenoids with their equally bulky power supplies. Thus, there has been increasing interest in the application of permanent magnet structures for such uses as electron-beam focusing and biasing fields. The current demand for compact, strong, static magnetic field sources that require no electric power supplies has created needs for permanent magnet structures of unusual form.
Various prior art structures have contributed to the development of technology in this area. For example, U.S. Pat. No. 4,701,737 to Leupold, entitled "Leakage-Free, Linearly Varying Axial Permanent Magnet Field Source" and U.S. Pat. No. 4,692,732 to Leupold et. al., entitled "Remanence Varying In A Leakage Free Permanent Magnet Field Source" (both incorporated by reference herein) both disclose magnetic circuits utilizing magnetic cladding means to reduce exterior flux leakage and increase the controlled magnetic field intensity. The advantageous features of this and similar devices are, significantly, the reduction of field loss and very effective control without any increase, in fact most times a decrease, in the size or weight of the magnetic circuit elements.
The present invention relates to applicants' co-pending application, Ser. No. 436,407 filed Nov. 14, 1989, entitled "Permanent Magnet Field Sources Of Conical Orientation" which is hereby incorporated by reference. A structure fabricated of magnetically rigid (MR) material combines a radial magnetic field source with an axial magnetic field source to produce a conical magnetic field source. MR materials are well known to those skilled in the magnetic arts. Some ferrites and rare-earth alloys have been utilized or are being contemplated for use as MR materials, such as barium ferrite, samarium cobalt and neodymium-iron-boron alloys. The most pronounced characteristic of MR materials is their very high coercivity (field magnitude required to demagnetize) relative to that of traditional magnetic materials. This characteristic affords the fabrication of structures that exhibit various magnetic circuit effects such as field transparency and flux confinement that are not attainable with traditional materials. As to field transparency, external magnetic fields up to some magnitude greater than the remanence (magnetized level) of MR material will pass therethorough without affecting the magnetic orientation thereof. A resultant field occurs equal to the vector sum of the external field and the field sustained by the MR material.
With respect to the flux confinement, the magnitude and direction of the magnetization is constant throughout any individual piece or segment of MR material. Therefore, a field source can be constructed of magnetic segments fabricated of MR material, to configure a magnetic circuit as desired and even to completely confine a whole magnetic circuit by enclosing a magnetic field in a cavity.